Canavanine-based assay for gross chromosomal rearrangements reveals hotspots and genome instability modulating genes in fission yeast

Deleting IR-LTRs reduces the GCR rate and reveals another hotspot driven by BIR between homeologous aldo/keto reductase genes on opposite arms of chromosome I. This is the first evidence that BIR can occur in S. pombe on long tracks reaching up to 600 kb. Besides highlighting genome rearrangement hotspots, the assay also identifies regulators of genome instability in fission yeast. Loss of Nup132, a component of the nuclear pore complex, increases IR-LTRs-induced GCRs, while the budding yeast homolog Nup133 has no effect on the stability of a structurally similar IR.

In contrast, disrupting djc9, which encodes a conserved histone H3–H4 binding protein, decreases GCR rates. Overall, this sensitive GCR assay enables the identification of factors that control spontaneous and fragile motif–induced chromosomal instability, including those conserved in humans but lost through evolution in other organisms.